From: Guo Ren <guoren@linux.alibaba.com>

Optimize arch_xchg|cmpxchg|cmpxchg_local with ASM acquire|release
instructions instead of previous C based.

The generic atomic.h used cmpxchg to implement the atomic
operations, it will cause daul loop to reduce the forward
guarantee. The patch implement csky custom atomic operations with
ldex/stex instructions for the best performance.

Important reference commit:
8e86f0b409a4 ("arm64: atomics: fix use of acquire + release for
full barrier semantics")

Changes in V3:
 - Add arch_atomic_(fetch_add_unless, inc_unless_negative,
   dec_unless_positive, dec_if_positive)

Changes in V2:
 - Fixup use of acquire + release for barrier semantics by Rutland.

Guo Ren (3):
  csky: cmpxchg: Optimize with acquire & release
  csky: atomic: Add custom atomic.h implementation
  csky: atomic: Add conditional atomic operations' optimization

 arch/csky/include/asm/atomic.h  | 249 ++++++++++++++++++++++++++++++++
 arch/csky/include/asm/barrier.h |  11 +-
 arch/csky/include/asm/cmpxchg.h |  64 +++++++-
 3 files changed, 316 insertions(+), 8 deletions(-)
 create mode 100644 arch/csky/include/asm/atomic.h

-- 
2.25.1